In the mid 1960's emission laws became a known factor that the automotive industry had to comply with. By 1970 the emission law had expanded to the fuel handling and containment system of the automobile. As the concern for air quality within the United States grew, more stringent emission laws were passed. In 1996, new emission laws were implemented called on-board diagnostics II, or OBDII. These new laws changed the regulations on the tailpipe emissions and the systems that were carried on the vehicle. The fuel handling and containment system would now have to test for electrical circuit problems, system operation, and system leakage. The system leakage from the containment system that would have to be found, and a diagnostic trouble code set for such leakage, would be a hole diameter greater than 0.040 of an inch or the equivalent of two or more holes that are equal or larger than the 0.040 spec. FIG. 1 shows some of the components of a basic OBDII fuel containment system. In the basic vacuum decay EVAP system shown in FIG. 1 there are two main control valves; purge control valve or solenoid (1) and vent control valve of solenoid (6). The purge control valve (1) is naturally closed and the vent control valve (6) is naturally open. The vent control valve (6) is open under all operational conditions until the on board computer (2) has determined the enabling criteria is correct to run a diagnostic test. At this time the vent valve (6) is turned on, this command closes the vent control valve, thus sealing the fuel containment and handing system from the atmosphere. The purge control valve (1) is then pulsed open and closed; this valve is connected to the engine intake manifold (4) where vacuum is present from a running engine. This vacuum pulls the air out of the fuel containment and handing system. As the air volume is removed, the system goes into a negative pressure (vacuum) state. This pressure s monitored by the engine control module (2) by using the fuel tank pressure sensor (8) located in fuel tank (10). The pressure in the fuel containment and handing system is pulled to a target pressure, usually about 7 inches of water column by turning the purge control valve (1) on and off. Once the target pressure has been reached the purge control valve (1) is turned off allowing it to close. The fuel containment and handing system is now sealed. The engine control module (2) monitors the fuel containment and handing system pressure using fuel tank pressure sensor (8). If there are no leaks present in the fuel containment and handing system the pressure will stay at the target pressure, approximately 7 inches of water column. This negative pressure is timed by the engine control module (2), if the pressure stays at the target pressure for a predetermined time there is no leakage present at the time the test was run. If the pressure decays (changes) in the clocked time period a leak or leaks are present within the system at the time the test was run. The amount of pressure decay from the fuel containment and handing system in the timed period will give the size of leakage from the system.
With this testing requirement of 0.040 of an inch diameter hole size, the automotive manufacturers would need to test at a smaller hole diameter than the specified hole size. This is due to a bell curve effect, which means that if the hole size was tested at the specified diameter, some of the failures would be assigned a pass and some a failure. Since the requirement is to make sure all leaks greater than 0.040 inch diameter produce a Diagnostic Trouble Code (DTC) to indicate an Evaporative Emission System (EVAP) failure, the leak test would have to be run for a hole size smaller than 0.040 of an inch. The hole size for the leakage test would be approximately a 0.030 inch hole in diameter. The leakage from this hole size is not a problem for the vehicle's onboard system to test and find, nor is this hole size a problem for off-board testing equipment to test and find, such as a smoke machine.
In the year 2000, new fuel containment leakage laws were implemented. The new laws cut the allowable leakage from the fuel containment system down to a hole size diameter of 0.020 of an inch. This is a 75% leakage testing reduction in the fuel containment system. This hole size diameter is very difficult for the vehicle's on-board system to find and code. New on-board systems would be implemented into the vehicle that could accurately detect this very small hole size diameter. However, due to the hole size and variables such as Reid Vapor Pressure (RVP) from the fuel, these new on-board systems can produce false diagnostic codes. The automotive industry's present off-board testing equipment, such as smoke machines, could no longer find and locate these very small hole diameters. The smoke or vapor that is produced by these machines, in perfect conditions, is hardly visible out of a 0.015 inch diameter size hole. In the automotive service bay, this vapor may not be detectable. This 0.015 inch diameter size hole is where these new vehicle containment systems are now testing at. This smaller than 0.020 hole size, approximately 0.015 of an inch, is once again used as the testing criteria due to the testing bell curve. The newest standard for evaporative emission containment systems is now the Partial Zero Emission Vehicle, or PZEV. This new standard is one in which the containment system is tested to a 0.008 inch diameter hole size, which is even harder to identify and locate.
What is needed in the automotive industry is a method that can be used off-board the vehicle to verify system leakage and then locate the point of such leakage. In the present invention, an off-board vacuum and pressure pump is used with a pressure transducer, reservoir chamber, and a calibrated orifice. The vacuum-pressure pump moves air into or out of the containment system, while the pressure transducer checks the pressure change over time to determine if the system is leaking. Once the system has determined that a leak is present, pressurized carbon dioxide (C02) is put into the containment system. A gas analyzer that can detect gasoline in the form of hydrocarbon (HC) and inert gas in the form of C02 is then used to locate the point of leakage from the vehicle's fuel containment system. A number of prior patents will now be briefly discussed.
In a patent by Reddy, U.S. Pat. No. 5,263,462, a vehicle on-board leak detection system is discussed that describes a way to find leaks in an EVAP system during engine-off periods.
In a patent by Reddy, U.S. Pat. No. 6,321,727, a vehicle on-board leak detection system is discussed that gave more control to his previous patent by the use of a solenoid control valve to control the fresh air vent.
In a patent by Fritz, U.S. Pat. No. 6,889,667, a vehicle on-board leak detection system is shown that uses an electric motor that drives a pump located in the venting valve. This pump pressurizes the fuel containment system. A calibration orifice is used to calibrate the electrical current of the pressure pump to a known leak size, and then a switching valve moves the calibration orifice out of the pump discharge and allows this pressure to fill the fuel containment system. The pressure pump electric current is checked and if it has less current than it had when pushing air through the calibration orifice a leak is present in the fuel containment system. This system test is run during engine-off periods.
In a patent by Kobayashi, U.S. Pat. No. 6,964,193, a vehicle on-board leak detection system is shown that uses an electric motor that drives a pump located in the venting valve. This pump puts the fuel containment system into a negative pressure. A switching valve is used with a calibration orifice. The pump pulls a vacuum against the calibration orifice while a pressure transducer is calibrated to this hole size diameter's pressure. The switching valve now switches the vacuum from the calibration orifice to the fuel containment system. The pressure transducer now monitors the pressure change in the fuel containment system. If the pressure is less than the pressure pulled against the calibration orifice, a leak is present in the fuel containment system. This system test is run during engine-off periods.
In a patent by Behar, U.S. Pat. No. 7,908,099, a vehicle on-board leak detection system is shown that uses a method on a running engine whereby the fuel (gasoline) is moved out of the fuel tank to the engine. As this fuel is removed from the tank, the vapor space within the fuel tank increases. Since a computer is injecting a known volume of fuel into the engine, this increase in vapor space within the fuel containment system is known. Two different calibration orifices of different sizes will be switched into the venting system creating a restriction. The pressure within the tank is read with a pressure transducer with each calibration orifice. This will indicate if a leak is present in the fuel containment system.
In a SAE technical paper, 1999-01-0861 by Delphi Automotive Systems, a vehicle on-board leak detection method is shown that uses a running engine that will supply the vacuum to the fuel containment system. This engine vacuum is sealed into the fuel containment system and watched by a pressure transducer to find small leaks. This system uses the vacuum decay rate to identify the presence of a leak within the fuel containment system.
In all of the prior art, the methods are quite different from the present invention. Some of the same components (e.g., calibration orifices, smoke generating devices) are implemented but the methods used are unique to the present invention. In the prior art, the systems are all on-board vehicle system testing units installed by the manufacturers to test the vehicle's fuel containment system. The invention is designed as an off-board system that checks the vehicle's onboard system and tests the vehicle's fuel containment system. However, many of the methods used in the present invention could be used with or as a part of a manufacturer's on-board fuel containment system test.